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Relationship Between Dike Injection and b-Value for Volcanic Earthquake Swarms
Journal of Geophysical Research: Solid Earth ( IF 3.9 ) Pub Date : 2021-11-13 , DOI: 10.1029/2020jb021631
Allen F. Glazner 1 , Stephen R. McNutt 2
Affiliation  

Dike swarms are the fossil remains of regions of the crust that have undergone repeated magma injections. Volcanic earthquake swarms and geodetic measurements are, at least in part, a record of active injection of fluids (water, gas, or magma) into fractures. Here, we link these two ways of observing magmatic systems by noting that dike thicknesses and earthquake magnitudes share similar scaling parameters. In the Jurassic Independence dike swarm of eastern California median dike thickness is ∼1 m, similar to other swarms worldwide, but glacially polished exposures reveal that a typical dike comprises a number of dikelets that are lognormally distributed in thickness with a mean of ∼0.1 m. Assuming that dikes fill penny-shaped cracks of a given aspect ratio, the geodetic moment and earthquake magnitude of a diking event can be estimated. A Monte Carlo simulation of dike-induced earthquakes based on observed dike thickness variations yields a frequency-magnitude distribution remarkably like observed volcanic earthquake swarms, with a b-value of ∼1.7. We suggest that swarms of dikes composed of dikelets, as well as plutons built incrementally by sheet intrusions, are physical complements to volcanic seismic swarms, and that at least some earthquake swarms are a palpable expression of incremental magma emplacement.

中文翻译:

堤防注入与火山地震群 b 值的关系

堤防群是地壳区域经历过多次岩浆注入的化石遗迹。火山地震群和大地测量至少部分是流体(水、气体或岩浆)主动注入裂缝的记录。在这里,我们通过注意到堤防厚度和地震震级共享相似的标度参数,将这两种观测岩浆系统的方法联系起来。在加利福尼亚东部侏罗纪独立堤坝群中,堤防厚度中值约为 1 m,与世界范围内的其他堤防群相似,但冰川抛光暴露表明一个典型的堤坝包括许多厚度呈对数正态分布的堤坝,平均厚度为 0.1 m . 假设堤坝填充了给定纵横比的便士形裂缝,则可以估计堤坝事件的大地力矩和地震震级。b值约为 1.7。我们认为,由堤坝组成的堤坝群,以及由片状侵入体逐渐建造的岩体,是火山地震群的物理补充,并且至少有一些地震群是岩浆侵位增量的明显表现。
更新日期:2021-12-04
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